This disclosure relates generally to a system and method for reducing NOx emissions in locomotives and vehicles that employ hydrocarbon-based fossil fuels, and more particularly, to a condenser unit for a NOx emission reduction system.
Production of emissions from mobile and stationary combustion sources such as locomotives, vehicles, power plants, and the like, has resulted in environmental pollution. One particular source of such emissions is NOx emissions from vehicles. Environmental legislation restricts the amount of NOx that can be emitted by vehicles. In order to comply with this legislation, efforts have been directed at reducing the amount of NOx emissions.
One method of emission reduction is directed to minimizing the amount of NOx emissions produced during the process of combustion in engines. This method generally involves redesigning engines to optimize the combustion of fuel. This approach has resulted in the reduction of NOx over the years; however, it is expensive and all efforts so far have not resulted in any substantial reduction in NOx emissions.
Another method is directed to using an ammonia selective catalytic reactor (SCR) to reduce NOx emissions. In this method, a solution of ammonia or urea contacts the exhaust stream of the combustion source to reduce the NOx to nitrogen over a SCR catalyst, water and carbon dioxide (if urea is used). This method is disadvantageous in that toxic chemicals such as ammonia or urea have to be carried on vehicles and maintained at sufficient levels for NOx reduction.
Yet another method is the “lean NOx trap” method that involves the dispersion of metal catalysts onto substrates such as, for example, barium oxide (BaO), calcium oxide (CaO) or barium carbonate (BaCO3) to form NOx traps which are placed in the exhaust stream of a vehicle engine. When, for instance, BaO is saturated with NOx thus forming barium nitrate, Ba(NO3)2, reductants are used to reduce the Ba(NO3)2 back to BaO and nitrogen. NOx emissions into the atmosphere are then reduced in this way. The cycle is then repeated. This method requires a large NOx trap often in a dual bed arrangement. For application on a locomotive or other mobile combustion sources, this method of reducing NOx would be too expensive and would take considerable space.
Furthermore, NOx SCR systems employing diesel fuel directly as the NOx reductant have been demonstrated in the past. However, straight injection of diesel fuel has shown to be inefficient because it causes coking on the SCR catalyst. In addition, when the exhaust temperature is low, injecting diesel fuel directly to the exhaust stream cannot reduce the NOx. Also, there has been application of lighter hydrocarbons, such as propane, as NOx reductants to the SCR system, but those concepts do not present feasibility for vehicular on-board systems.
It is therefore desirable to have a fuel conversion system that does not require carrying toxic chemicals, and avoids the development of expensive infrastructure for reductant distribution. Furthermore, a need exists for techniques for generating NOx reductants while increasing fuel efficiency of the fuel conversion system.